High speed valves are commonly employed in applications where the flow of a gas or gases into a vessel, such as a vacuum chamber, must be controlled very rapidly. Although the design details of high speed valves vary, most include a valve member in the form of a disc which is spring-biased to seal an orifice from a plenum into which the gas is admitted. The valve member is usually fabricated from aluminum or a similar material in which an eddy current is induced by passing a time varying current in a planar coil located in proximity therewith to lift the valve member away from the orifice. As long as a time varying current is present in the coil, the valve member continues to be lifted from the orifice to open the valve. An example of a high speed valve of this type is found in British Patent Specification No. 953,476.
Present day high speed gas valves only produce a single stream of gas. In certain applications, there is a need to rapidly control the flow of a gas to produce a plurality of gas streams which form a shell. For example, with certain types of plasma x-ray sources, there is a need to produce a plurality of gas streams to form a gas shell which can be ionized when an electric field is applied axially thereacross. When ionized, the shell is transformed into a sheath of plasma which carries a current axially along its surface.
The current passing in the plasma sheath produces a magnetic field which interacts therewith to produce a radially inwardly directed force which implodes the sheath. Upon implosion, the sheath of plasma becomes very hot and dense, causing electrons therein to move to higher energy levels. The electrons ultimately jump to lower energy levels, causing the plasma to radiate energy in a burst of soft x-rays. An example of a plasma x-ray source which produces x-rays in this fashion is found in copending application Ser. No. 727,470 for "Method and Apparatus for Producing X-ray Pulses" filed on Apr. 26, 1985 in the name of B. Kuyel and assigned to the same assignee. That appplication is herein incorporated by reference.
Accordingly, there is a need for a technique for rapidly controlling the flow of gas to produce a plurality of gas streams which form the outline of a shell.